gpui: Update docs to reflect removal of View, ViewContext, WindowContext (#24008)

This PR updates function signatures, docstrings, and gpui's other
documentation to reflect it's new state following the merge of `Model`
and `View` into `Entity` as well as the removal of `WindowContext`.

Release Notes:

- N/A

crates/gpui/src/platform/mac/window.rs

@@ -949,7 +949,7 @@ impl PlatformWindow for MacWindow {
         unsafe { self.0.lock().native_window.isKeyWindow() == YES }
     }
 
-    // is_hovered is unused on macOS. See WindowContext::is_window_hovered.
+    // is_hovered is unused on macOS. See Window::is_window_hovered.
     fn is_hovered(&self) -> bool {
         false
     }